Kaposi's sarcoma-associated herpesvirus (KSHV), or human herpesvirus 8 (HHV 8), is invariably present in Kaposi's sarcoma (KS) lesions where it has been localized in the endothelial cells as well as in the spindle cells, which are thought to be of endothelial cell origin. We have been able to reproducibly infect primary human endothelial cells with KSHV, and obtained apparently immortalized endothelial cell cultures as a direct result of this infection. The KSHV-infected endothelial cells are transformed as defined by their anchorage independent growth, prolonged survival and telomerase activity. This provides the first direct demonstration that KSHV is an oncogenic virus, and probably represents the best in vitro system developed thus far to study the pathobiology of Kaposi's sarcoma. However, the mechanism of transformation utilized by KSHV appears to be different from that of other oncogenic viruses, since only a small proportion of the cells in these cultures retain the viral genome. Preliminary evidence has suggested that paracrine mechanisms play an important role in the long term survival induced by KSHV, but that the viral genome is necessary for full transformation. Our overall objective is to test this hypothesis by using in vitro infection of endothelial cells to analyze the mechanism(s) of transformation of endothelial cells by KSHV and the role of angiogenesis in this process. Specifically, we plan: (Aim number 1 )to characterize the paracrine mechanisms responsible for the long term survival of endothelial cells; (Aim number 2) to assess the direct effect of KSHV in transformation; (Aim number 3) to assess the HIV/KSHV interactions in endothelial cell cultures, and (Aim number 4) to develop a mouse model for the study of KS. The results of these experiments should allow us to better understand the process of infection and transformation by KSHV. The information gained will contribute to our understanding of the pathogenesis of Kaposis sarcoma, and will aid in the development of rational therapeutic and preventive approaches. These studies will also provide information that will enrich our general knowledge of viral oncogenesis.